This invention relates to bushing assemblies for use with a movable shaft. More particularly, it relates to use of such assemblies in power generating apparatus such as gas turbine engines.
Most modern designs of axial flow gas turbine engines include the capability to vary the position of certain stationary airfoils or vanes in respect to the airflow through the engine. Early examples of gas turbine engines including such variable mechanisms, typically in the engine compressor section, are shown in U.S. Pat. No. 2,858,062--Allen (patented Oct. 28, 1958); and U.S. Pat. No. 2,933,235--Neumann (patented Apr. 19, 1960). In addition, such variable mechanisms have been used in other parts of the engine, for example in the inlet, in front fans, in aft fans, in sections of the engine downstream of the compressor, and their combinations.
One form of a gas turbine engine compressor variable stator vane assembly uses a shaft, sometimes called a torque shaft, in an actuation system to move groups of vanes in a designed manner. Movement of the shaft, at least one end portion of which is carried in a slot loaded spherical bearing assembly, includes at least partial rotation of the shaft as well as some shaft excitation resulting from normal operation and rotation of the engine. Such action on the combination of a shaft end portion and bearing assembly has resulted in significant wear of the shaft end portion requiring replacement of the entire shaft more frequently than desired.